1. Field of the Invention
The present invention relates to a pretensioner which is a portion of a seat belt device which restrains a vehicle occupant by a webbing belt.
2. Description of the Related Art
On a webbing belt which is configured as an elongated strip which restrains a vehicle occupant, or the so-called seat belt device, a pretensioner is provided. When the vehicle rapidly decelerates or is in some other predetermined state, the pretensioner increases the restraining power by forcefully rotating the winding shaft which is anchored to a longitudinal end portion of the webbing belt, in the direction in which the webbing is taken up.
The general structure of the above mention pretensioner will be explained below.
The pretensioner is provided with a cylinder which is a cylindrical configuration having a bottom. A piston is accommodated in an inner portion of the cylinder. At an opening end side of the cylinder, a rack bar is integrally formed with an end portion of the piston. At the side of the rack bar, a pinion gear which engages with the rack bar is disposed. The pinion is mechanically connected to the winding shaft by means of a one way clutch. The piston moves in the direction of the opening end side of the cylinder, and the rack bar by rotating the pinion, forcefully rotates the winding shaft in a take-up direction.
At a side portion of the main body portion of the cylinder where the piston is accommodated, the generator accommodating portion is integrally connected with the main body portion of the cylinder, and the main body portion and the generator accommodating portion, together form the cylinder. The generator accommodating portion is a cylindrical configuration having both ends open. One end corresponds with the inner portion of the cylinder main body portion at the vicinity of the bottom portion thereof. Meanwhile, a gas generator is fitted in from the other end portion. The gas generator is a cylindrical form whose outer diameter dimension is slightly smaller that the inner diameter dimension of the generator accommodating portion. In the inner portion thereof, a gas generating agent which by combustion instantaneously generates a predetermined amount of gas and an ignition device for igniting the gas generating agent is accommodated. When the gas generating agent is combusted, gas is instantaneously provided between the bottom portion of the cylinder (main body portion) and the piston and it is the gas pressure of this gas by which the piston is pressed.
The ignition device is connected to a separately provided acceleration sensor either directly, or indirectly through a computer or some other control device. When the acceleration sensor detects a rapid deceleration of the vehicle, the ignition device operates.
In the pretensioner of the prior art described above, the axial direction of the cylinder accommodating portion is orthogonal to the axial direction of the cylinder main body portion. Consequently, even if the inner diameter dimension of the main body portion of the cylinder is small, the overall size of the cylinder cannot be small because of the effect of the length in the axial direction of the generator accommodating portion. If as in this manner, the pretensioner is large overall, when the cylinder is mounted to the vehicle, it is possible that it will interfere with the structural components of the vehicle. Choice in terms of a position for installing the pretensioner becomes limited and in some cases installation itself becomes difficult.
Further, in the pretensioner of the prior art, when the generator accommodating portion accommodates the gas generator, a stopper whose outer diameter dimension is large with respect to (that is, larger than) that of the main body portion of the gas generator determines the position of the gas generator. Correspondingly, at the other end portion of the generator accommodating portion a large diameter portion which is large enough to allow the stopper to fit is formed. This large diameter portion has an inner diameter dimension larger than the inner diameter dimension at the portion where the main body of the gas generator is accommodated. The stopper is accommodated at this large diameter portion and by abutting the bottom portion of the large diameter portion (that is, the portion defined by the large diameter portion and the portion which accommodates the main body portion of the gas generator), determines the position of the gas generator.
In this case, it is necessary for the outer diameter dimension of the generator accommodating portion to be sufficiently larger than the outer diameter dimension of the stopper. This causes the generator accommodating portion to be large and the pretensioner to be bulky.
In view of the above, an object of the present invention is to obtain a compact pretensioner.
A first embodiment of the present invention, is a pretensioner for use with a winding shaft and a webbing belt having an end, with the end anchored to the winding shaft, the pretensioner being for applying rotational force during a predetermined condition to the winding shaft, in a take-up direction for winding the webbing belt, the pretensioner comprising:
(a) a cylinder main body having an interior with a piston movably disposed therein, wherein gas pressure in the cylinder main body causes the piston to move in a direction for supplying rotational force to the winding shaft in a take-up direction for winding the webbing belt;
(b) a generator accommodating portion disposed generally as a cylinder integrally extending from the cylinder main body, the cylinder main body having a bottom, with an opening located between the piston and the bottom of the cylinder main body, the opening being connected in fluid communication with the cylinder of the generator accommodating portion; and
(c) a gas generator mountable to said generator accommodating portion for generating gas under a predetermined condition, and supplying gas pressure for causing piston movement.
In a pretensioner with the above structure, under a predetermined condition, gas is generated in the gas generator and when the gas is supplied to the interior of the cylinder main body, the gas pressure (inner pressure) of the cylinder main body increases, thereby pressing the piston and causing the piston to move toward one axial direction end side thereof. This movement of the piston causes the winding shaft to rotate in the take-up direction. Consequently the force with which a vehicle occupant is restrained by the webbing belt increases.
Further, when this pretensioner is compared with a structure in which the axial direction of the generator accommodating portion is set in the direction orthogonal to the axial direction of the cylinder main body, since the axial direction of the generator accommodating portion thereof is inclined at the axial side of the cylinder main body from the direction orthogonal to the axial direction (the axial orthogonal direction) of the cylinder main body, if the axial direction dimensions of the generator accommodating portions are the same in the two cases, the other axial end portion of the generator accommodating portion (that is, the end portion at the side opposite the cylinder main body) is positioned nearer to the cylinder main body side in the present invention. For this reason, the dimension of the pretensioner which is set in the direction orthogonal to the axial direction of the cylinder main body becomes smaller, thus allowing the pretensioner to be compact.
Also, in the pretensioner of the present invention, a space is generated at the bottom portion side of the cylinder main body along the axial orthogonal direction of the cylinder main body from which the generator accommodating portion is inclined. Therefore, the pretensioner is more compact in this respect as well. Thus, even if a structural component of the vehicle is positioned at this portion, there are no bad effects when the pretensioner is mounted to a vehicle. Therefore assembly is facilitated and choice in terms of the position for mounting the pretensioner is increased.
In a second aspect of the present invention, the generator accommodating portion includes an end, and when the gas generator is mounted to the generator accommodating portion, the gas generator includes a protruding portion having an external periphery with a stopper formed thereon, with the stopper abutting the end of the generator accommodating portion.
According to this aspect, the stopper which is provided to the gas generator abuts the other end portion of the generator accommodating portion and thereby restricts the displacement of the gas generator. Due to this structure, the outer diameter dimension of the stopper may be smaller than the outer diameter dimension of the gas generator, provided that the outer diameter dimension of the stopper is larger than the inner diameter dimension of the gas generator. In addition, since the stopper does not have to be accommodated inside the generator accommodating portion, the thickness of the generator accommodating portion can be reduced. As a result, in the pretensioner based on the present aspect, the generator accommodating portion is more compact and this causes the pretensioner to be light and compact.
In a third aspect of the present invention, the generator accommodating portion and cylinder main body each have a center axis, which are skewed relative to one another. In the pretensioner based on this aspect, the center axis of the generator accommodating portion when extended does not coincide with the center axis of the cylinder main body. Thus, since the opening radial direction of the portion connecting the cylinder main body and the generator accommodating portion is inclined with respect to the opening radial direction of the generator accommodating portion, the opening radius of the connecting portion is larger than the opening radius of the generator accommodating portion. This results in the opening area of the connecting portion being large. Accordingly, it is possible to ensure a sufficient opening area for the connecting portion without placing the external periphery of the generator accommodating portion lower toward the outer bottom portion of the cylinder main body. That is, the pretensioner is more compact.
In a fourth aspect of the present invention, the cylinder main body has an opening end side with a thickness less than a thickness of the bottom of the cylinder main body. Due to this structure, the cylinder main body becomes compact and light and this contributes to the pretensioner as a whole being compact and light.
When the gas pressure of the gas supplied to the cylinder main body is at a maximum, because the piston is in the start position, the high gas pressure is basically exerted only in the vicinity of the bottom portion of the cylinder main body. However, when the piston rises due to an increase in internal pressure, the space in the inner portion of the cylinder main body increases relative to the volume of gas generated, causing the internal pressure to decrease. As a result, the gas pressure exerted at the opening end side of cylinder main body is not as much as the gas pressure exerted at the bottom portion side where the initial phase of gas generation occurs. Therefore, making the cylinder main body thin does not affect mechanical strength.
To summarize, according to the present aspect, in the vicinity of the bottom portion of the cylinder where a large amount of gas pressure is exerted, thickness and mechanical strength is ensured. Meanwhile, at the opening end portion side where comparatively little gas pressure is exerted, the thickness is reduced. Thus the pretensioner is compact and at the same time the necessary mechanical strength is ensured.
In a fifth aspect of the present invention, the above-described pretensioner further comprises a rack (bar) and pinion meshed with one another, with the pinion coupled to the winding shaft and the rack extending from the piston, wherein the rack moves with the piston, thereby rotating the pinion and applying rotational force to the winding shaft in the take-up direction for winding the webbing belt
In a pretensioner with the above-described structure, when the piston moves due to increased internal pressure of the cylinder main body, the rack bar which is provided at one axial direction end portion of the piston rotates the pinion which meshes with the rack bar. The rotation of the pinion at this stage is transmitted to the winding shaft and rotates the winding shaft in the direction in which the webbing is taken up.